100 SPECIES OF THE SYSTEMA. 
must be preferred, since that species was constituted at an 
earlier period. M. Deshayes, however, thus distinguishes the 
two: glycimeris, he asserts, has its valves depressed, and its 
interior quite white; its ligamental area, moreover, is smaller 
and narrower, and its concentric striz more conspicuous than 
in pilosus ; the latter he characterises as having its valves more 
inflated and brown, with the longitudinal strie upon them 
equally conspicuous with those which decussate them; the 
interior, besides, is stained with brown at the posterior 
extremity. 
Areca wewnearta. 
The box thus marked in the Linnean cabinet contains some 
young specimens of the Pectunculus violascens (Payraud. Moll. 
Cors. pl. 2, f. 1), which agree with the description and assigned 
locality of the A. nwmmaria. In his own copy of the ‘ Systema; 
our author has written “ Pet. Gaz. t. 52, f. 7,” in which work is 
delineated a Mediterranean shell of the size and shape of the 
original examples. 
The species, as it appeared in print, not being ade- 
quately defined, and the description being unsuitable to 
mature individuals, the name nwmmaria has no valid claim 
to precedence. 
Arca wielets. 
The definition of this shell is so utterly insufficient, that one 
wonders how ever its modern genus, and far more its species, 
could have been divined. Tradition points out the Nucula 
nucleus (Brit. Moll. pl. 47, f. 7, 8) for its representative, and this 
is confirmed in some measure by the reference “ Pet. Gaz. t. 17, 
f. 9” (usually cited for nucleus, yet almost as like radiata, or 
nitida) added in the Linnean copy of the ‘Systema.’ There 
are a few worn, bleached, uncoated single valves of a Nucula 
(one of the three mentioned) in a paper marked A. nucleus in 
the Linnean collection, but the writing is not that of our 
